IMRT: bending radiotherapy beams to spare healthy cells

Part three of our new blog series on radiotherapy explores a type of radiotherapy treatment called IMRT. We cover what it is, how it’s already improved the lives of many patients and why this number will continue to grow.

A tumour is a 3D ball of cells, each with a unique shape and position in the body. This causes a problem for radiotherapy as some parts of the tumour may be closer to healthy tissues than others.

The stronger the radiotherapy beam the more damage it will do to normal cells, which increases side effects and the chance of scarring.

So radiotherapists have borrowed a trick from the theatre.

Just as leading actors get a strong spotlight on stage with the rest of the set lit less brightly, different parts of a tumour can get different intensities of radiotherapy.

The advanced technique that lets this happen is called intensity modulated radiotherapy (IMRT), where the intensity of radiation varies depending on which part of the treatment area it hits.

To each according to his needs

The crux of IMRT treatment is to give each part of the tumour enough radiation to kill it but to protect healthy cells at the same time.

This is done by using a bit of high-tech kit in the radiotherapy machine called a multileaf collimator. The radiation beam passes through metal leaves that slide to make different shapes.

The collimators movement is unique to each patient and controls the area exposed to radiation as well as the direction and intensity of the beam. This means that the precious, normal tissues get a much lower dose.

When it first came about IMRT was given by using many beams, each from a different direction. The patient lay on the bed whilst the radiotherapy machine sat in fixed positions, pointing to the tumour in the middle.

The idea is that the beam hits the tumour at lots of different angles but doesn’t stay in contact with healthy cells for long, so they have an easier job of recovering. Because this process is repeated from lots of different angles, the radiation beam has great coverage of the tumour but spares the important organs and normal cells around it.

A more sophisticated way of receiving IMRT is becoming increasingly available. Now the most modern radiotherapy machines deliver radiation in a smooth arc around the patient, which shortens the time it takes to give the treatment.

IMRT in the clinic

During IMRT the radiotherapy machine is a great multitasker. It moves around the patient changing the shape of the beams and their intensity, depending on which area of the body it’s treating.

“The way the beams shape and intensity changes, means it can spare areas of the body that don’t need radiation. For example, when we treat tumours in the pelvis it avoids sensitive areas like major nerves or genitals.” says Sebag–Montefiore.

Sebag–Montefiore thinks developments in IMRT have significantly improved treatment options for patients and their quality of life.

“IMRT has dramatically changed our ability to treat some cancers more effectively. It’s a type of radiotherapy treatment that can offer much more individualised treatment and gives the right dose to the right target,” he says.

All tumours are different shapes and sizes, so each patient gets their own individual programme of radiation.

Transforming lives

“We used to operate on cancers of the head and neck and remove the tumours with surgery, but this is such a delicate area the operation would cause a lot of physical and psychological damage,” says Sebag–Montefiore.

With IMRT, just the tumour and a small area around it are exposed to radiation, reducing side effects and scarring.

IMRT is also improving quality of life for patients with anal cancer. With reproductive organs, the lower intestines and the bladder very near, operating is tricky.

“In anal cancer, surgery used to be thought of as the best treatment, but the whole back passage would be removed and a patient would have to use a colostomy bag for the rest of their life,” says Sebag–Montefiore.

IMRT has dramatically changed our ability to treat some cancers more effectively.

– Professor David Sebag-Montefiore

But IMRT’s beams are so carefully controlled delicate nerves around the bladder and genital area get less radiation, so anal cancer can be cured with fewer side effects.

“Because of this, the standard of care has changed for this cancer from chemo and surgery to radiotherapy,” he says.

There are many trials underway testing the best ways to use IMRT for a variety of cancers.

For example, the PLATO trial is using IMRT to decide the best radiotherapy treatment for patients with anal cancer.

Researchers are also looking at whether IMRT could help really hard to treat cancers. The SCALOP2 trial is looking at the best radiotherapy dose to use in patients with pancreatic cancer that hasn’t spread and how best to combine it with drugs.

Professor Corrine Faivre-Finn thinks IMRT could be particularly useful in killing non-small cell lung cancer (NSCLC). She’s a Cancer Research UK expert in radiotherapy and is looking into the impact of IMRT on lung cancer at The Christie hospital in Manchester.

Her team looked back on nearly 9,000 lung cancer patients treated with IMRT between 2005 and 2015. They found that, as time went by, the number of patients that had radiotherapy treatment with the intention to cure increased each year. Before the introduction of IMRT in 2008, the number of patients given radiotherapy to cure was at 39 in 100 patients. But once it was fully available between 2009-2012 this number rose to 59 in 100.

“This means that IMRT has let us treat large volumes of tumours and tumours near organs that in the past we wouldn’t have been able to treat. We would have just given them end-of-life care or low doses of radiotherapy.” says Fairve-Finn.

But she adds that it’s not just survival that’s important.

“If you give a treatment like this you can control the disease for longer. This means less symptoms and so a better quality of life for the patient.”

Personalising treatment

Both Sebag–Montefiore and Faivre-Finn think patients will be having more and more personalised treatment plans using IMRT.

It’s clear that IMRT has already put on a pretty impressive show. In the case of lung cancer, it’s meant that larger, more developed tumours – previously thought too advanced to treat – can now be treated. It’s also changed practice for a number of cancer types.

And with further improvements on the way, IMRT could be set to take centre-stage in more treatment plans, for more cancer types in the future.

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